To extend the functionality of you web application relative to your requirements you are supposed to use existing yii core libraries or use external libraries. There are some steps to ensure security, uniqueness, modularity, performance and to avoid rework in future.

After installing Yii basic application on our systems, most of the time we want to have multiple environment such as local, dev and live setup. Most of the times when we want to make changes to configuration file, we have to over-write configurations file for each environment.